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Old 05-07-2005, 12:24 AM   #1
manman99
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Default UTEC Closed and Open Loop Fueling

Hi,
confused over close and open loop fueling,
hope someone can help clear my doubt.

If I buy a new UTEC now, i will be getting the new version 4.2c.

Does it mean below 25% TPS ----> closed loop fuleing
over 25% TPS ----> Open loop fueling ?

And I can change the default of 25% TPS at one of the user
parameters ?

Thks

Cheers
lam
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Old 05-07-2005, 02:44 AM   #2
AWDWRXLOVER
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Is open or close loop better? Its on closed now. I just installed a stage 4 (vf39, pinks, fp) and have some issues at high rpm. The utec was bought used and is on the old 3.1 or 3.2 version. Should I update the utec to the 4.2? I did some test runs today and it shows my duty cycle at 99- 100 at 16-17.5 psi. How is this possible? The only thing my friend could come up with is that on my version there isnt a spot to tell the utec what size injectors im using, so maybe the car thinks it has stocks in it and there is too much fuel. Any help info would be great.
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Old 05-07-2005, 03:01 AM   #3
hippy
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Here's a link with wrx fueling and other stuff in it. I think it would be wise if you updated the firmware to 4.2c.

peace
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Old 05-07-2005, 11:27 AM   #4
manman99
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Smile

Hi Hippy,

Thks for the reply. After reading your link (Great info),
still not able to find the answer to the question.

If I buy a new UTEC now, i will be getting the new version 4.2c.

Does it mean below 25% TPS ----> closed loop fuleing
over 25% TPS ----> Open loop fueling ?

And I can change the default of 25% TPS at one of the user
parameters ?
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Old 05-07-2005, 11:43 AM   #5
serendipity
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Quote:
Originally Posted by manman99
Hi Hippy,

Thks for the reply. After reading your link (Great info),
still not able to find the answer to the question.

If I buy a new UTEC now, i will be getting the new version 4.2c.

Does it mean below 25% TPS ----> closed loop fuleing
over 25% TPS ----> Open loop fueling ?

And I can change the default of 25% TPS at one of the user
parameters ?
Yes.

And to respond to the other poster, the choices are NOT between Closed and Open Loop Fueling. Open Loop Fueling is really a misnomer. It should be called something like "standalone fueling".

Here's a quick breakdown for a stock ECU:
Below ~60% throttle and some RPM (5kish), the car is in closed loop. That means it targets a stoich (14.7:1) air/fuel mixture.
Above that throttle or RPM, the car switches to Open Loop, meaning it uses its own fuel map, with some corrections that it learned in Closed Loop mode, to determine fueling. It ignores the AFR Sensor.

Old UTEC (before OLF):
Above the TPS Switchover Threshold (60% by default), the UTEC would move from the 0% column to the 10% column in your timing and fuel maps. It would drive timing directly, and apply whatever fuel change was in the map to the MAF sensor voltage going to the ECU. It's still the ECU that decides how much fuel to use, based on its own fuel map + its own corrections (learned during closed loop operation) + UTEC's correction (this is oversimplified, since the UTEC doesn't directly change fuel, but it works for this explanation).

With this setup, your fueling is inconsistent, since it depends on what the car learns during closed loop operation. In addition, on 04+ cars, there is a significant delay between crossing the throttle threshold and the stock ECU actually going into open loop mode. This means the UTEC might have been using the corrections from your map to the MAF sensor voltage, but the stock ECU is still running in closed loop mode, so the car would stay at stoich while you were under boost. Again, fueling is inconsistent.

You also couldn't just change the threshold to some much lower value (typically), because your fuel corrections would sometimes be applied while the car is in closed loop, and sometimes in open loop. So Part Throttle Full Boost problems still strike here since the car will be shooting for stoich and you have little control below the ECU's switchover from Closed -> Open loop.

With OLF (more properly called Standalone Fueling or something to that effect), the UTEC has ITS OWN fuel map, similar to the stock ECUs. Instead of just passing a modified MAF sensor voltage to the stock ECU, the UTEC ignores the ECU's calculations, and uses its own map. This results in an instantaneous switchover when you cross the TPS threshold, since the UTEC takes over completely for fuel and timing. In addition, because it's not depending on the stock ECU, you can pick a much lower threshold and not have to worry about the stock ECU trying to run stoich at full boost at 50% throttle for example.


OLF/Standalone Fueling is better than CLF in my opinion, in all cases. It's much more controllable.

The holy grail would be Closed Loop Fueling everywhere - so you just pick an AFR target for each RPM and Load site in the map, and the car figures out how to hit that. This is very processor intensive and tends to be a slow process since the ECU has very little time in each site to see what the AFR is and apply a small correction to get it to the target.
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Old 05-07-2005, 12:20 PM   #6
MMBOOST
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Best explanation of OLF vs CLF I ever read, by Jarrad@PDXtuning.com. At the start he's discussing my change of the threshold point from 25% to 30%, but by the the third paragraph is gets good.

http://www.wrxhackers.com/forums/sho...27&postcount=9
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Old 05-08-2005, 03:48 AM   #7
manman99
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Hi Guys, thks for the info. understand better now..
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Old 05-08-2005, 12:24 PM   #8
hippy
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I forgot to mention that utecs olf mode isn't supposed to be used with wrx's that have automatic trannies. If you have one, then don't use utecs olf mode.

peace
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Old 05-09-2005, 10:45 AM   #9
manman99
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Default

Hi Hippy,

Mine is manual.. you are great help!!!
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